High efficiency preambles for communications systems over pseudo-stationary communication channels

ABSTRACT

A method includes appending a preamble to a data packet and transmitting the preamble and data packet over a communication channel in the network. The preamble may be a Beacon, Admission, Broadcast, or High-Throughput Preamble. The Beacon Preamble includes the following symbols SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, LS 1 , LS 1 , LS 1 , LS 1 , LS 1 , LS 1 , LS 1 , LS 1 , CP 0 , CE Beacon , CE Beacon . The Admission Preamble includes the following symbols SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, LS 1 , LS 1 , LS 1 , LS 1 , LS 1 , LS 1 , LS 1 , LS 1 , CP 0 , CE, CE. The Broadcast Preamble includes the following symbols LS 1 , LS 1 , LS 1 , LS 1 , CP 0 , CE, CE. The high-throughput preamble includes the following symbols CP 0 , CE. The SS symbol includes 64 bits, the LS 1 , LS 2 , and CP 0  symbols include 192 bits, the CE symbol includes 512 bits, and the CE Beacon  symbol is a subset of CE.

RELATED APPLICATIONS

The application claims the benefit of U.S. provisional application No.61/096,268 filed Sep. 11, 2008, entitled “High efficiency preambles forcommunications systems over pseudo-stationary communication channels”,and U.S. provisional application No. 61/096,435 filed Sep. 12, 2008,entitled “Parametric construction of PHY-frame preambles on coax”, andU.S. provisional application No. 61/145,076 filed Jan. 15, 2009,entitled “High efficiency preambles for communications systems overpseudo-stationary communication channels.

FIELD OF DISCLOSURE

The disclosed system and method relate to the transmission of datathrough a network. More particularly, the disclosed system and methodrelate to transmitting data through an orthogonal frequency divisionmultiplexed (OFDM) network with high-efficiency preambles.

BACKGROUND

In a conventional Multimedia Over Coaxial Alliance (MoCA) network, datapackets are transmitted over a coaxial communication channel. Each datapacket in a conventional MoCA network includes a preamble followed by adata payload. The preambles are used to calibrate the receiver toreceive the following data with the appropriate gain, phase andfrequency compensation. The preambles are also used by the receiver todetermine when the first OFDM symbol of the payload will be received atthe receiver.

FIG. 1 illustrates five different preambles 102, 122, 132, 142, 152 offour different lengths that are utilized in a conventional MoCA 1.0network. Each preamble is made up of some combination of Short Segments(SS), Long Segments (LS), Gaps, Cyclic Prefixes (CP), and ChannelEstimation Symbols (CE).

Each SS segment is defined by a 30-bit binary data input sequence, suchas {0111 0000 1000 0111 1100 0100 1111 10}. Each bit of the binary datainput sequence is modulated using π/4—offset Bi-Phase Shift Key (BPSK)modulation.

Each LS segment is defined by one of two 64-bit binary data inputsequences: LS1, having a binary sequence such as {1111 1101 0101 01100100 0100 1011 0110 0011 1010 0001 1010 1110 0111 1011 1110} and LS2,having a binary sequence such as {1011 1001 1110 1111 1000 0001 01010011 0010 0010 0101 1011 0001 1101 0000 1101}. As is the case with theSS, each bit of the binary data input sequence of the LS is modulated asa π/4—offset BPSK modulation. As noted in FIG. 1, half of the LSsegments that are used in a Long Sequence 106 are inverted (as noted bythe negative sign shown for LSs of the second half of the Long Sequence106).

Each Gap consists of 32 in-phase and quadrature zeros at a nominalsample rate of 50 MHz.

Each CP is a repeat of the end of the symbol at the beginning. Thepurpose is to allow multipath to settle before the main data arrives atthe receiver. The receiver is normally arranged to decode the signalafter it has settled because this avoids inter-symbol interference. Thelength of the cyclic prefix is often equal to the duration of thechannel impulse response.

Each CE is a 256-bit binary data sequence in which each bit is modulatedon one of the 256 active sub-carriers. The bit sequence is, for example,the binary sequence expressed in hexidecimal notion as {ABD2 F451 90AE61E1 D660 D737 3851 2273 6DE9 86E5 B401 CCC6 8DC1 2613 E116 0E2E} wherethe first bit in the sequence is assigned to the 0th sub-carrier and thelast bit is assigned to the 255th sub-carrier.

The preamble lengths are varied to maximize the available bandwidth fordata transmission. As shown in FIG. 1, the two most robust preambles arethe Beacon Preamble 102 and the MAP Preamble 122. The Beacon Preamble102 and the MAP Preamble 122 are the most robust and least efficientpreambles because they are used for network coordination and containinformation concerning the network. The second most robust preamble typeis the Admission/Probes Preamble 132. The Admission/Probe Preamble 132is used by a transmitter to accommodate a receiver that has little-to-noa priori information about the communication link over which thetransmitter will transmit data. The second most efficient preamble isthe Broadcast/Data Preamble 142. The Broadcast/Data Preamble 140 is usedto transfer data from a transmitter to one or more receivers and assumesthe receiving node has some a priori information about the communicationlink. The most efficient, and thus shortest, preamble is theHigh-Throughput Unicast Data (HTUD) Preamble 152. The HTUD Preamble 152is appended to the beginning of a data packet when the receiver has asubstantial amount of a priori information about the communicationchannel.

Beacon Preamble

In a conventional MoCA network, a Beacon 100 is transmitted at regularintervals by the network's Network Controller (NC). In some embodiments,the NC transmits a Beacon 100 every 10 ms. A node attempting to join anexisting MoCA network may scan for a Beacon 100, which provides networkinformation such as the channel time clock (CTC), the MoCA networkversion, and the time of the next admission control frame (ACF) in thedata payload 160. Once a node has joined a MoCA network, the node usesthe Beacons 100 to track the CTC, determine when the next MAP 120occurs, and to track a NC handoff, e.g., when the NC changes from onenode to another node.

As shown in FIG. 1, the Beacon Preamble 102 includes a Short Sequence104 followed by a Long Sequence 106. An Access ID 108 follows the longsequence 106 and precedes a Channel Estimation Training Sequence 110.The data payload 160 follows the Channel Estimation Training Sequence110.

The Short Sequence 104 comprises twelve SS segments, each of which iscomprised of 30 time domain samples at a sample rate of 50 MHz. Inaccordance with one embodiment of the disclosed method and apparatus,the Short Sequence 104 is used by a receiving node for making automaticgain control (AGC) adjustments. There are two scenarios in which aBeacon 100 may be received at a receiving node. In one scenario, thereceiving node is attempting to join the MoCA network. Accordingly, thenode will have no information about the network and the Short Sequence102 is used to accommodate the AGC adjustments that may be required bythe joining node. In the second scenario, the node is already connectedto the network and thus the node will likely need to make few if any AGCadjustments since the NC regularly transmits messages through the MoCAnetwork.

Long Sequence 106 comprises eight LS1 segments, each of which arecomprised of 64 time domain samples at a sample rate of 50 MHz. In oneembodiment of the disclosed method and apparatus, the Long Sequence 106is used by a receiving node for burst detection, frequency estimation,deriving packet start time, and making a final AGC adjustment asdescribed in greater detail below.

Access ID 108 includes an SS segment, a Gap, and an LS4 segment. The Gaphas a length of 32 samples at a sample rate of 50 MHz, and is generatedby setting the voltage on the communication link to zero volts.

The Access ID 108 of the Beacon Preamble 102 is used by a node searchingfor a Beacon 100 when attempting to join a MoCA network. For example,after burst detection has been performed by a receiving node, thereceiving node will validate the Access ID 108. The validation of theAccess ID 108 is accomplished by correlating the LS4 segment against astored reference of the LS4 segment. If the Access ID 108 is notvalidated by the receiving node (e.g., there is a poor correlationbetween the stored reference value and incoming LS4 segment), then thereceiving node will assume that burst detection occurred either on thepreamble of a non-Beacon packet or was falsely detected. The receivingnode will then reset the burst detector and continue searching for theBeacon 100 rather than continuing to process the packet. If the Beacon100 is detected, then the receiving node will know a priori when thenext Beacon 100 will arrive and validation of the Access ID 108 is notrequired.

The Channel Estimation Training Sequence 110 includes a cyclic prefix CPhaving a length of 64 samples at a sample rate of 50 MHz, plus anadditional 32 samples at a sample rate of 50 MHz. The cyclic prefix CPand 32 additional samples are followed by two channel estimationsymbols, CE. The Channel Estimation Training Sequence 110 is used forestimating the characteristics of the communication link or channelbetween two nodes. The cyclic prefix CP and the 32 additional samples inconjunction with the 126 samples of the Access ID 108 ensure that theburst detection and packet start time computations (e.g., when the datapacket 160 will be received) are complete prior to the arrival of thechannel estimation symbols, CE. In accordance with one embodiment of thedisclosed method and apparatus, the two CE symbols are used to start thefrequency and timing tracking loops of the receiving node.

MAP Preamble

MAPs 120 are broadcast packets sent by the NC to all of the networknodes to provide scheduling information and are transmitted on afrequent basis. In some MoCA networks, the MAPs 120 are transmitted bythe NC approximately every 1 ms on average. The MAPs 120 identify wheneach network node is scheduled to transmit data through the network. Asshown in FIG. 1, the MAP Preamble 122 is identical to the BeaconPreamble 102 with the exception of an LS3 segment being used instead ofan LS4 segment. Descriptions of the like components of the MAP Preamble122 are omitted to avoid redundancy.

A network node distinguishes a MAP 120 from a Beacon 100 by the outcomeof the correlation of the LS segment of the Access IDs 108, 124.Accordingly, the LS3 and LS4 segments correlate against one anotherpoorly so that a receiving node may easily distinguish between a MAP 120and a Beacon 100.

Admission/Probe Preamble

Admission packets 130 are transmitted prior to a link profile beingestablished for a node being admitted to the network. Accordingly, anAdmission packet 130 is transmitted when a network node has little to noinformation concerning the communication link between it and theadmitting network node. In these scenarios, the first Admission packet130 is transmitted in an admission request, which has a scheduled timeslot as identified by the Beacon or MAP packet 120. The Probes 130 aretransmitted by each of the network nodes and are used to characterizecommunication channels between the transmitting network node and each ofthe other nodes connected to the network. The Probes 130 are transmittedat regular intervals between each of the network nodes.

As shown in FIG. 1, the Admission/Probe Preamble 132 is similar to theBeacon and MAP Preambles 102, 122 with two exceptions. One differencebetween the Admission/Probe Preamble 132 and the Beacon and MAPPreambles 102, 122 is that the Admission/Probe Preamble 132 does notinclude an Access ID 108, 124. The second difference between theAdmission/Probe Preamble 132 and the Beacon and MAP Preambles 102, 122is that the cyclic prefix CP of the Channel Estimation Training Sequence134 is followed by 100 additional 50 MHz samples as opposed to the 32additional 50 MHz samples implemented in the Beacon and Admission/ProbePreambles 102, 122.

The processing and use of the Short Sequence 104 and Long Sequence 106of the Admission/Probe Preamble 132 are utilized by a receiving node inthe same manner in which they are used by a receiving node receiving aBeacon or MAP Preamble 102, 122. Similar descriptions are not repeated.

The 100 additional samples that follow the cyclic prefix CP in theAdmission/Probe Preamble 132 are implemented to ensure that the burstdetection and packet start time computation performed by a receivingnode are completed prior to the arrival of the channel estimationsymbols CE. The CE symbols are used to start the frequency and timingtracking loops of the receiving node.

Broadcast Data Preamble

The Broadcast/Data Preamble 142 is attached to the beginning of all datapackets that are broadcast by a network node. The Broadcast/DataPreamble 142 is shorter in length than the Beacon, MAP, andAdmission/Probe Preambles 102, 122, 132 because the receiving nodes willhave some information concerning the communication channels throughwhich they will receive the data.

As shown in FIG. 1, the Broadcast/Data Preamble 142 includes a MediumSequence 144 followed by a Channel Estimation Training Sequence 134.Medium Sequence 144 includes a single SS segment used for AGC adjustmentfollowed by four LS1 segments, which in accordance with one embodimentof the disclosed method and apparatus, are used to perform a final AGCadjustment, burst detection, frequency estimation, and to derive thestart time of the data.

The Channel Estimation Training Sequence 134 includes the cyclic prefixCP and 100 additional 50 MHz samples followed by two CE symbols. The 100samples that follow the CP ensure that burst detection and packet starttime computations performed by receiving nodes is completed prior to thearrival of the channel estimation symbols, CE, which are used to startthe frequency and timing tracking loops of the receiving node.

HTUD Preamble

The HTUD Preamble 152 is the most efficient Preamble and is reserved forunicast data transmission between nodes having considerable a prioriinformation concerning the communication channel through which theycommunicate. As shown in FIG. 1, the HTUD Preamble 152 includes an LS2segment followed by the Channel Estimation Training Sequence 134.

The LS2 segment of the HTUD Preamble 152 is used for burst detection andderiving the start time of the data. Frequency estimation and AGCadjustments are not performed as the receiving nodes rely on a priorigain and frequency estimates to maximize data throughput.

While preambles are necessary to calibrate the receiver and identify thestart of the data, they take up valuable network bandwidth and reducethe throughput of the communication channel.

Accordingly, high-efficiency preambles for communication systems overpseudo-stationary communications systems are desirable.

SUMMARY

A method and apparatus is disclosed herein for transmitting a datapacket through a network, including appending a preamble to the datapacket and transmitting the preamble and data packet over acommunication channel in the MoCA network. In accordance with oneembodiment, the preamble is one or more of a Beacon, Admission,Broadcast/Unicast, MAP or High-Throughput Preamble. The Beacon Preambleincludes the following symbols SS, SS, SS, SS, SS, SS, SS, SS, SS, SS,SS, SS, LS₁, LS₁, LS₁, LS₁, LS₁, LS₁, LS₁, LS₁, CP₀, CE_(Beacon),CE_(Beacon). The Admission Preamble includes the following symbols SS,SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, LS₁, LS₁, LS₁, LS₁, LS₁,LS₁, LS₁, LS₁, CP₀, CE, CE. The MAP Preamble includes the followingsymbols SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, LS₂, LS₂, LS₂,LS₂, LS₂, LS₂, LS₂, LS₂, CP₀, CE, CE. The Broadcast Preamble includesthe following symbols LS₁, LS₁, LS₁, LS₁, CP₀, CE, CE. The UnicastPreamble includes the following symbols CP₀, CE, CE. The MAP Preambleincludes the following symbols LS₂, LS₂, LS₂, LS₂, CP₀, CE, CE. TheHigh-Throughput Preamble includes the following symbols CP₀, CE. The SSsymbol is defined by 64 bits, the LS₁, LS₂, and CP₀ symbols are eachdefined by 192 bits, the CE symbol is defined by 512 bits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates conventional preambles used in a MoCA 1.0 network.

FIG. 2 illustrates one embodiment of high-efficiency preambles inaccordance with the present disclosure.

FIG. 3 illustrates a simplified architecture of a transmission channeland a receiving channel of a MoCA 2.0 node in accordance with thepresent disclosure.

DETAILED DESCRIPTION

High-Efficiency Preambles

The MoCA 1.0 preambles illustrated in FIG. 1 and described above havebeen the industry standard for several years. However, these preamblesinclude inefficiencies that restrict the maximum obtainable throughputof a MoCA network.

The high-efficiency preambles described in detail below perform similarfunctions to those of the MoCA 1.0 preambles, but enable a higherthroughput, more accurate power estimation and more accurate burstdetection times, compared to the preambles of MoCA 1.0. Additionally,the data throughput of a MoCA network can be further increased by usingranging. For example, ranging enables a receiving node to predict when apacket will arrive by determining the distance between itself and thetransmitting node. Accordingly, ranging enables a receiving node tonarrow the window in which it looks to receive an incoming data packetas the receiving node will be able to determine when the packet shouldarrive.

Beacon Preamble

FIG. 2 illustrates one embodiment of high-efficiency preambles 202, 212,222, 232 in accordance with the present disclosure. In accordance withone embodiment, as shown in FIG. 2, a Beacon Preamble 202 may include aShort Sequence 204 followed by a Long Sequence 206. In one suchembodiment, a Channel Estimation Correlation Sequence 208 and a datapayload 260 follow the Long Sequence 206. In one embodiment, such aBeacon Preamble 202 is used when all of the nodes in the network will becapable of detecting this Beacon Preamble 202. That is, this BeaconPreamble 202 is best used in networks in which legacy devices that canonly detect MoCA 1.0 Beacons 100 (shown in FIG. 1) are not permitted tojoin as nodes to the network. Alternatively, in some embodiments of thedisclosed method and apparatus, the Beacon 100 is used in place of themore efficient Beacon 200 to allow legacy nodes to join the network.

In some embodiments, the Short Sequence 204 includes twelve “SS”Orthogonal Frequency Division Multiplexed (OFDM) symbols, each definedby 64 frequency domain bits. That is, each SS symbol is generated byusing a 64-bit data sequence that is Bi-Phase Shift Key (BPSK) modulatedonto 64 sub-carriers spaced over 100 MHz. In one particular embodiment,the spacing is even. Alternatively, the spacing can be selected toachieve a particular purpose. Each BPSK modulated sub-carrier istranslated to the time-domain using a 64-point Inverse Fast FourierTransform (IFFT). The samples from each of the 64 sub-carriers aresummed in a parallel to serial converter to obtain one complex sample.Sixty-four such samples comprise an SS symbol. The time domain samplesare generated at a 100 MHz sample rate. Accordingly, each samplerepresents the complex summation of all 64 sub-carriers over a discreteperiod of time equal to 1/(100⁶) sec. The Short Sequence 204 consists of12 such SS symbols. In accordance with one embodiment, each SS symbol isgenerated using the following short sequence (starting at sub-carrier 0through sub-carrier 511 in steps of 8):SS=[x001 0000 1111 1010 1101 0001 0011 101x xx00 0101 1110 0010 11011010 0001 0000];

where a ‘0’ represents the BPSK point {+1, 0}, a ‘1’ represents the BPSKpoint {−1, 0}, and an ‘x’ represents {0, 0}. Additional detailsregarding the generation of the preambles are presented below withregard to FIG. 3.

The Long Sequence 206 includes eight “LS₁” symbols, each of which, inaccordance with one embodiment of the disclosed method and apparatus,are defined by 128 frequency domain bits.

In accordance with one embodiment, LS₁ is generated using the followinglong sequence (starting at sub-carrier 0 through sub-carrier 511 insteps of 4):LS₁=[x010 1011 1001 0010 1010 1011 1000 1001 0011 1001 0111 1100 11001001 0110 1xxx xxxx 1111 0000 0110 1000 0001 1111 1100 1101 0101 11101111 1010 0011 0001 0000],

where a ‘0’ represents the BPSK point {+1, 0}, a ‘1’ represents the BPSKpoint {−1, 0}, and an ‘x’ represents {0, 0}. Accordingly, sub-carrier 0(the first sub-carrier) is modulated with x, sub-carrier 3 is modulatedwith a zero, sub-carrier 7 is modulated with a one, sub-carrier 10 ismodulated with a zero, etc.

In one embodiment, the content of the Long Sequence 206 can be unique tothe Beacon Preamble, and so a receiver can use the content of the LongSequence 206 to identify the Beacon Preamble as such.

A Channel Estimation Correlation Sequence 208 includes a cyclic prefix“CP₀” followed by two Beacon Channel Estimation Sequences,“CE_(Beacon)”. Each CE_(Beacon) is defined by 512 frequency domain bits.In some embodiments, the cyclic prefix CP₀ has a length of 128 frequencydomain bits. In an alternative embodiment of the disclosed method andapparatus, the length is 192 frequency domain bits. It will beunderstood by those skilled in the art that other lengths are possibleas well.

A receiving node uses the Channel Estimation Correlation Sequence 208 tomeasure the channel response (the response of the communication channelbetween nodes), such that the channel's effects can be compensated forwhen decoding the data symbols. In addition, the channel estimationsymbols are used to make long-term AGC energy measurements and toestimate the frequency offset (if two CE symbols are transmitted). Itshould be noted that one difference between the Channel EstimationCorrelation Sequence and the MoCA 1.0 Channel Estimation TrainingSequence 110 shown in FIG. 1 is that in the presently disclosed methodand apparatus, the symbols of the Channel Estimation CorrelationSequence 208 are transmitted on all available sub-carriers. That is, inaccordance with one embodiment of the presently disclosed method andapparatus, the Channel Estimation Correlation Sequence is transmitted onsub-carriers 4 thru 243 and 263 thru 508 (480 total sub-carriers). Incontrast, MoCA 1.x mandated that the channel estimation symbols betransmitted on used sub-carriers only. Transmitting on all availablesub-carriers (a) improves the performance of channel smoothing, (b)results in a constant and thus predictable channel estimation symbol,which is important for burst detection performance and (c) eliminatesdegenerate cases where the elimination of particular sub-carriers causesthe Peak-to-Average Ratio (PAR) to exceed the transmitter clippingratio. The PAR is measured as the magnitude (I²+Q²).

The Short Sequence 204 of the Beacon Preamble 202 may be used by areceiving node for AGC adjustments. Long Sequence 206 of Beacon Preamble202 may be used by a receiving node to perform minor AGC adjustments,burst detection, frequency estimation, and deriving the start time ofthe data payload 260.

As shown in FIG. 2, the improved Beacon Preamble 202 does not include anAccess ID 108 (seen in FIG. 1). In some embodiments of MoCA, the AccessID 108 was intended to be used by a receiver to distinguish a Beaconpacket from a MAP packet. When looking for an asynchronous Beacon (i.e.when the arrival time of the Beacon is unknown), the Access ID was usedto distinguish the Beacon from MAP packets and Admission/Probe packets.Note that for packets being transmitted in a MoCA network, all packetsother than the Beacon are synchronous. Accordingly, the receiver knows apriori what packet type is going to be received and thus ignores theAccess ID. In accordance with one embodiment of the presently disclosedmethod and apparatus, the CE_(Beacon), or some subset thereof, is usedas a Channel Estimation Correlation Sequence 208 to distinguish thepackets of a Beacon 200 from other packets, thus allowing theelimination of the Access ID 108 from the presently disclosed method andapparatus. Eliminating the Access ID 108 from the Beacon Preamble 202provides improved data throughput through the communication channel.

Additionally, eliminating the Access ID 108 and implementing a 192sample CP₀ enables a receiving node to better estimate the energy of theincoming packet. As described above, the Access ID 108 of the MoCA 1.0Beacon Preamble 102 begins with a 32 sample SS symbol followed by a zerovolt Gap. Due to signal processing delays, a receiving node mayfrequently underestimate the power of the incoming packet as the energymeasurements performed during the AGC adjustments would include aportion of the Gap, resulting in a power underestimation ofapproximately 1 dB, depending upon the implementation.

The improved Beacon Preamble 202 of the presently disclosed method andapparatus enables more accurate power estimation by eliminating theAccess ID 108 and providing a cyclic prefix CP₀, which may have one ormore non-zero values. Accordingly, if a receiving node experiencessignal processing delays, the non-zero volt values of the cyclic prefixCP₀ eliminate the power underestimation by the receiving node.

In one embodiment of the disclosed method and apparatus, a ChannelEstimation Correlation Sequence 208 may be used by a receiving node todistinguish a Beacon from other packets, e.g., validate that the packetis in fact a Beacon 200. Receiving nodes may determine that a preambleis a Beacon Preamble 202 because the Beacon Preamble 202 is the onlypreamble that includes a Beacon Channel Estimation (CE_(Beacon)) symbol.For example, a receiving node may correlate the received CE_(Beacon)symbol against the symbol it expects to receive in a Beacon Preamble.The results of the correlation of the CE_(Beacon) and the referencesymbol will identify whether the received preamble was a BeaconPreamble, as described in greater detail below. In one embodiment, thereceiver looks for whether a CE symbol is received. If a CE symbol wasnot received, the receiving node determines that the preamble is aBeacon Preamble 202 as it is the only preamble that does not include theCE symbol, but rather includes a CE_(Beacon) symbol.

In another embodiment of the disclosed method and apparatus, in additionto, or instead of, using a unique channel estimation symbol, a differentset of LS symbols (i.e. LS₁ vs. LS₂) can be used for Beacons.

Admission/Probe Preamble

As shown in FIG. 2, an Admission/Probe Preamble 212 may include theShort Sequence 202 including a plurality of SS symbols followed by theLong Sequence 214 including a plurality of LS₁ symbols. The LongSequence 214 may be followed by a Channel Estimation and TrainingSequence 216 that may include the cyclic prefix CP₀ and two channelestimation symbols, CE.

One embodiment of the disclosed method and apparatus uses the followingCE symbol (starting at sub-carrier 0 through sub-carrier 511):CE=[xxxx 1011 1101 0010 1111 0100 0101 0001 1001 0000 1010 1110 01100001 1110 0001 1101 0110 0110 0000 1101 0111 0011 0111 0011 1000 01010001 0010 0010 0111 0011 1111 0011 0000 1110 1011 1100 0001 0010 00100101 1010 1110 1001 1100 1000 1110 0000 0011 1010 1000 0111 1011 01011110 1110 0011 1100 0100 1011 xxxx xxxx xxxx xxxx xxxx xxxx x001 00101011 0100 1000 1001 0010 0000 0011 1111 1001 0100 0111 0010 1100 00101001 1101 1100 1100 0111 0110 0000 1100 0111 0010 0110 0110 1100 01101101 1110 1001 1000 0110 1110 0101 1011 0100 0000 0001 1100 1100 11000110 1000 1101 1100 0001 0010 0110 0001 0011 1110 0001 0001 0110 00001110 0010 1xxx]

where a ‘0’ represents the BPSK point {+1, 0}, a ‘1’ represents the BPSKpoint {−1, 0}, and an ‘x’ represents {0, 0}. Using the hexadecimalnotation of MoCA 1.x, this can be written as:CE=[ABD2 F451 90AE 61E1 D660 D737 3851 2273 F30E BC12 25AE 9C8E 03A87B5E E3C4 Bxxx xxx1 2B48 9203 F947 2C29 DCC7 60C7 266C 6DE9 86E5 B401CCC6 8DC1 2613 E116 0E2E]

The first and last 128 sub-carriers have the same CE symbol as definedby the industry standard MoCA 1.x (i.e., MoCA 1.0, 1.1, . . . etc.);only the center 256 sub-carriers are newly defined. This reduces thememory requirements and control logic for generating the CE symbol.

The channel estimation symbols shall modulate all of the availablesub-carriers and not just those sub-carriers which are used by aparticular packet. For example, if a particular sub-carrier is bitloadedto zero due to low signal-to-noise ratio or other considerations, thechannel estimation symbol shall still transmit that sub-carrier.

In some embodiments, the LS₂ symbol may be used instead of LS₁ symbol.In embodiments in which a Beacon 200 is used, the CE_(Beacon) symbol maybe used by a receiving node to distinguish between a Beacon 200 and anAdmission/Probe 210.

MAP Preamble

In a MoCA network, MAP packets 120 are transmitted as broadcast messagesto each node connected to the network. Accordingly, in one embodiment,the improved high-efficiency preambles include a single preamble that isused for both the MAP packets and broadcast packets. However, as shownin FIG. 2, a MAP Preamble 215 may include a Medium Sequence 223including a plurality of the LS₂ symbols. The LS₂ symbols are unique tothe MAP Preamble and allow the receiver to distinguish the MAP packetsfrom all other types of packets.

In accordance with one embodiment of the disclosed method and apparatus,use the following long sequence (starting at sub-carrier 0 throughsub-carrier 511 in steps of 4):LS2=[x101 1100 0001 1010 0100 1011 1011 1001 0011 0101 1101 0000 10000101 0011 0xxx xxxx 1111 0010 1000 0111 0011 0011 0111 0101 0110 10011111 0011 1011 1000 1000]

where a ‘0’ represents the BPSK point {+1, 0}, a ‘1’ represents the BPSKpoint {−1, 0}, and an ‘x’ represents {0, 0}.

The Medium Sequence 223 is followed by a Channel Estimation TrainingSequence 226. The Channel Estimation Training Sequence 226 may include acyclic prefix CP₀ and the channel estimation symbol CE. In someembodiments, a second CE symbol may follow the first CE symbol.

In accordance with the presently disclosed method and apparatus, the MAPpacket is sent relatively frequently. Thus, in accordance with thepresently disclosed method and apparatus, the receiver gains a highconfidence in the channel characteristics from these frequently receivedMAP packets. By relying upon the information gathered from previouslysent packets, the short sequence of the MAP packets of the presentlydisclosed method and apparatus are not required to be used for AGC orfrequency estimation given that the gain and frequency offsets can beeasily be inferred from previous transmissions and tracked on the manyMAP packets being generated and received. Therefore, the MAP Preamble ofthe presently disclosed method and apparatus does not have SS symbols.Furthermore, the number of LS symbols is reduced in the MAP Preamble 215shown in FIG. 2 to four from the eight that are provided in the MAPPreamble 120 shown in FIG. 1.

Accordingly, the improved MAP Preamble 215 is significantly shorter thanthe MAP Preamble 122 shown in FIG. 1, thereby reducing the amount ofdata transmitted through a network. The savings in bandwidth issignificant, as MAPs 120, 220 are frequently transmitted by the NC toother nodes. Additionally, the frequency with which a MAP 120, 220 istransmitted by an NC enables the MAP Preamble 222 to be shortenedbecause the receiving node will likely not need to make AGC adjustmentsas it will have a priori information concerning the characteristics ofthe transmission channel between itself and the transmitting node.

Broadcast and Unicast Preamble

The Broadcast and Unicast Preamble 220 shown in FIG. 2 has essentiallythe same format as the MAP Preamble 215 with the exception of using LS₁symbols rather than LS₂ symbols in the Medium Sequence 224.

HTUD Preamble

As shown in FIG. 2, the HTUD Preamble 232 may include a ChannelEstimation Training Sequence 226 comprising the cyclic prefix CP₀followed by the channel estimation symbol CE. The HTUD Preamble 232 mayinclude the cyclic prefix CP₀ followed by the channel estimation symbolCE. In some embodiments, a second channel estimation symbol CE mayfollow the first CE symbol.

The improved HTUD Preamble 232 eliminates the need for an LS₂ symbolpreceding the Channel Estimation Training Sequence 134 in the HTUDPreamble 152 shown in FIG. 1. HTUD packets 150, 230 are the most commonpackets transmitted in a MoCA network. Thus, the reduced length of theHTUD Preamble 232 increases the amount of data transmitted in thenetwork and increases throughput. It should be noted that the LS₂ symbolcan be eliminated because, in accordance with one embodiment of thepresently disclosed method and apparatus, burst detection is performedby a receiving node correlating a known symbol with a portion of thechannel estimation symbol, CE (or, alternatively, the entire symbol).This may require some buffering of the channel estimation symbol in thereceiver, however, given that these packets are the predominant packettype, the improved throughput benefit will typically outweigh the costsof buffering.

Transmission and Receiver Processing Channel

FIG. 3 illustrates one example of a node 300 of a MoCA communicationnetwork coupled through the communication link 315 to a second node 320in the MoCA communication network. In accordance with one embodiment ofthe disclosed method and apparatus, the node 300 includes a preamblegenerator 301 that receives a serial bit stream of frequency domain databits. The serial bit stream is coupled to the preamble generator fromeither a preamble sequence source 303 or a payload data source 305. Thenode 300 includes a serial-to-parallel (S2P) block 302, a QAM map 304,an Inverse Fast Fourier transform (IFFT) block 306, parallel-to-serial(P2S) block 308, and a CP inserter block 310. The S2P 302 receives andassigns each of the frequency domain data bits to one of a plurality ofsub-carriers of a carrier signal, as illustrated in FIG. 3, by theplurality of outputs emanating from the S2P block 302.

In some embodiments, the serial stream of bits provided by the preamblesequence source 303 provides a bit stream that defines portions of eachof the preambles 202, 212, 222, 232 shown in FIG. 2. Those portions ofthe bit stream include a 512-bit channel estimation sequence thatdefines the CE symbols, a 128-bit LS sequence that defines the LSsymbols and a 64-bit SS sequence that defines the SS symbols. The serialbit stream is modulated by the QAM map 304 using BPSK. Each bit of the512-bit channel estimation sequence is assigned to a unique one of thesub-carriers; each bit of a 128-bit LS sequence is assigned to everyfourth sub-carrier (the remaining sub-carriers are not modulated); andeach bit of a 64-bit SS sequence is assigned to every eighth sub-carrier(the remaining sub-carriers are not modulated). One skilled in the artwill understand that other modulation techniques including, but notlimited to, 16-bit quadrature amplitude modulation (16-QAM), 32-QAM,64-QAM, 128-QAM, 256-QAM or the like, may be used.

The QAM MAP block 304 is configured to modulate each bit on eachsub-carrier. For example, if a preamble is modulated using BPSK, then a‘0’ may be modulated onto 1, +j, a ‘1’ may be modulated onto −1, −j andan “unmodulated” sub-carrier may be “modulated” to 0, 0j. The bits ofthe data payload 260 are modulated using the appropriate QAMconstellation as understood by one skilled in the art. This is done bymodulating every N^(th) sub-carrier (i.e., N=1, 4, 8) with one bit ofthe frequency domain bit stream. The IFFT block 306 converts thefrequency-domain OFDM symbol output by the QAM map 304 into a stream ofparallel time-domain symbols comprised of a parallel set of time domainsamples at a sample rate of 100 MHz. The parallel time-domain symbolsoutput by the IFFT block 306 are N repetitions of a 1/N-length sequence.For example, if the SS sequence includes 64-bits and every eighthsub-carrier is modulated, then a 512-sample output of the IFFT block 306consists of eight identical repetitions of a 64-sample sequence.Likewise, every fourth sub-carrier is modulated for a 128-bit LSsequence resulting in the output of the IFFT block 306 being fouridentical repetitions of a 128-sample sequence.

The parallel-to-serial (P2S) block 308 converts the output of the IFFTblock 306 into a sample stream for transmission over the communicationlink 315. The CP inserter block 310 may repeat portions of the OFDMsymbols in order to provide guard time between symbols to protectagainst inter-symbol interference (ISI). For example, the CP inserterblock 310 repeats preamble sequences, such as the 512-sample cyclicprefix CP.

The receiving channel 320 includes a receiver section 321. The receiversection 321 typically will include an analog-to-digital converter (ADC)322 configured to receive the analog signal from the communicationchannel 315 and convert it to a digital signal. It will be understood bythose skilled in the art that the receiver section 321 will typicallyalso include frequency conversion and filtering (not shown in FIG. 3).However, in alternative embodiments, the receiver section may includeonly some of these components as necessary to receive and initiallyprocess the incoming received signals. The digital signal is received atan automatic gain controller (AGC) 324, which measures the energy of thereceived preamble 202, 212, 222, 232 and adjusts the gain of thereceiver section (and more particularly in one embodiment, the ADC 324)such that the dynamic range of the data packet 260 fits within thedynamic range of the ADC 322 so that the data may be properly processed.

In one embodiment of the disclosed method and apparatus, across-correlator 326 compares a stored 2-bit quantized reference of eachsample of the CE symbol with the output of the ADC 322. In some suchembodiments, the quantized reference may be a −1, 0, or a +1 as −2 isnot used. The cross-correlator 326 performs a cross-correlation bymultiplying each 2-bit value of the stored quantized reference by thecorresponding sample of the received quantized symbol. Once each complexsample of the received signal has been multiplied by its corresponding2-bit complex value in the quantized reference, the magnitude of thecomplex result is obtained. If the magnitude is a large number, thenthere is a good cross-correlation. However, if the magnitude is a smallnumber, then there is a poor cross-correlation. In accordance with oneembodiment, the cross-correlator 326 is used to detect whether aCE_(Beacon) has been received.

The burst detector 328 of receiver processing channel 320 may performburst detection to detect the presence of the CE symbol in the receivingchannel 320. For example, burst detection may be performed by observinga succession of linearly increasing peaks output from thecross-correlator 326.

The high-efficiency preambles described above enable higher datathroughputs to be achieved in MoCA networks. In some embodiments,throughput increases of approximately 5-26 megabits per second (Mbps)may be realized, which is a substantial increase due to the bandwidthlimitations of coaxial networks (i.e., networks in which nodes areconnected to one another over coaxial cabling).

In addition to the above described embodiments, the disclosed method andsystem may be embodied in the form of computer-implemented processes andapparatus for practicing those processes. The present disclosed methodand apparatus may also be embodied in the form of computer program codeembodied in tangible media, such as floppy diskettes, read only memories(ROMs), CD-ROMs, hard drives, “ZIP™” high density disk drives, DVD-ROMs,blu-ray drives, flash memory drives, or any other computer-readablestorage medium, wherein, when the computer program code is loaded intoand executed by a computer, the computer becomes an apparatus forpracticing the disclosed method and system. The present disclosed methodand apparatus may also be embodied in the form of computer program code,for example, whether stored in a storage medium, loaded into and/orexecuted by a computer, wherein, when the computer program code isloaded into and executed by a computer, the computer becomes anapparatus for practicing the disclosed method and apparatus. Whenimplemented on a general-purpose processor, the computer program codesegments configure the processor to create specific logic circuits.

Although the invention has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed broadly, to include other variants and embodimentsof the invention, which may be made by those skilled in the art withoutdeparting from the scope and range of equivalents of the invention.

1. A method of transmitting an admission data packet through a coaxial network, comprising: a) generating an Admission Preamble including the following symbols SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, SS, LS₁, LS₁, LS₁, LS₁, LS₁, LS₁, LS₁, LS₁, CP₀, CE, CE; b) appending the Admission Preamble to a data payload; and c) transmitting the admission data payload and appended Admission Preamble over coaxial cable in a MoCA network; wherein: i) the SS symbol is defined by a 30-bit binary data input sequence, ii) the LS₁ symbol is defined by a 64-bit binary data input sequence, iii) CP₀ is a repeat of the end of the symbol, iv) CE is a 256-bit binary data sequence in which each bit is modulated on one of a plurality of active sub-carriers, v) generating comprises using the following short sequence: SS=[x001 0000 1111 1010 1101 0001 0011 101x xx00 0101 1110 0010 1101 1010 0001 00001; and wherein: vi) generating comprises using the following CE symbol: CE=[xxxx 1011 1101 0010 1111 0100 0101 0001 1001 0000 1010 1110 0110 0001 1110 0001 1101 0110 0110 0000 1101 0111 0011 0111 0011 1000 0101 0001 0010 0010 0111 0011 1111 0011 0000 1110 1011 1100 0001 0010 0010 0101 1010 1110 1001 1100 1000 1110 0000 0011 1010 1000 0111 1011 0101 1110 1110 0011 1100 0100 1011 xxxx xxxx xxxx xxxx xxxx xxxx x001 0010 1011 0100 1000 1001 0010 0000 0011 1111 1001 0100 0111 0010 1100 0010 1001 1101 1100 1100 0111 0110 0000 1100 0111 0010 0110 0110 1100 0110 1101 1110 1001 1000 0110 1110 0101 1011 0100 0000 0001 1100 1100 1100 0110 1000 1101 1100 0001 0010 0110 0001 0011 1110 0001 0001 0110 0000 1110 0010 1xxx] to generate each CE symbol; and vii) a ‘0’ represents the BPSK point {+1, 0}, a ‘1’ represents the BPSK point {−1, 0}, and an ‘x’ represents BPSK point {0, 0}.
 2. A method of transmitting broadcast and unicast data packets through a coaxial network, comprising: a) generating a Broadcast and Unicast Data Preamble including the following symbols LS₁,LS₁, LS₁, LS₁, CP₀, CE; b) appending the Broadcast and Unicast Data Preamble to a data payload; and c) transmitting the data payload and appended Broadcast and Unicast Data Preamble over a communication channel in a MoCA network; wherein: i) the LS₁ symbol is defined by a 64-bit binary data input sequence, ii) CP₀ is a repeat of the end of the symbol, iii) CE is a 256-bit binary data sequence in which each bit is modulated on one of a plurality of active sub-carriers; iv) generating comprises using the following long sequence: LS₁=[x010 1011 1001 0010 1010 1011 1000 1001 0011 1001 0111 1100 1100 1001 0110 1 xxx xxxx 1111 0000 0110 1000 0001 1111 1100 1101 0101 1110 1111 1010 0011 0001 00001 to generate each LS₁ symbol; and v) generating comprises using the following CE symbol: CE=[xxxx 1011 1101 0010 1111 0100 0101 0001 1001 0000 1010 1110 0110 0001 1110 0001 1101 0110 0110 0000 1101 0111 0011 0111 0011 1000 0101 0001 0010 0010 0111 0011 1111 0011 0000 1110 1011 1100 0001 0010 0010 0101 1010 1110 1001 1100 1000 1110 0000 0011 1010 1000 0111 1011 0101 1110 1110 0011 1100 0100 1011 xxxx xxxx xxxx xxxx xxxx xxxx x001 0010 1011 0100 1000 1001 0010 0000 0011 1111 1001 0100 0111 0010 1100 0010 1001 1101 1100 1100 0111 0110 0000 1100 0111 0010 0110 0110 1100 0110 1101 1110 1001 1000 0110 1110 0101 1011 0100 0000 0001 1100 1100 1100 0110 1000 1101 1100 0001 0010 0110 0001 0011 1110 0001 0001 0110 0000 1110 0010 1xxx] to generate each CE symbol and vi) a ‘0’ represents the BPSK point {+1, 0}, a ‘1’ represents the BPSK point {−1, 0}, and an ‘x’ represents BPSK point {0, 0}. 